Control apparatus for supplying operating potentials

ABSTRACT

There is disclosed a system for supplying operating potentials which is particularly useful with load devices wherein at least two transversely oriented conductors are dielectrically isolated from a gaseous discharge medium between the conductors. The system utilizes a wave form generator having at least one output transistor. Novel transformer-diode clamping means are provided to reverse bias the collector-base junction of the output transistor. The transformer-diode clamping means is responsive to the removal of a turn-on signal and the saturation of the transistor to automatically reverse bias the collector-base junction to provide a system which produces a more effective wave form. The wave form in the embodiment shown is used as a sustaining voltage for cells in a gas discharge display/memory panel. This embodiment of the transformer-diode clamping means is particularly effective when connecting the output of the wave form generator to ground.

Peters Nov. 5, 1974 CONTROL APPARATUS FOR SUPPLYING OPERATING POTENTIALS[75] Inventor: Edwin F. Peters, Maumee, Ohio [73] Assignee:Owens-Illinois, Inc., Toledo, Ohio [22] Filed: Dec. 8, 1972 [211 App].No.: 313,349

[52] US. Cl 307/268, 307/237, 307/263, 315/169 TV [51] Int. Cl.. [103k17/04, G06k 15/18, 1-105b 41/29 [58] Field of Search 315/169 TV, 169 R;307/268, 261, 263, 280, 237

[56] References Cited UNITED STATES PATENTS 3,155,921 11/1964 Fischman307/261 X 3,470,391 9/1969 Granger 307/268 X 3,588,597 6/1971 Murley315/169 3,654,388 4/1972 Slottow et al. 315/169 TV 3,700,928 10/1972Milberger et al. 307/268 3,706,023 12/1972 Yamada et al. 315/169 TVPrimary ExaminerRudolph V. Rolinec Assistant Examiner-William D. LarkinsAttorney, Agent, or Firm-Donald Keith Wedding [57] ABSTRACT Thereisdisclosed a system for supplying operating potentials which isparticularly useful with load devices wherein at least two transverselyoriented conductors are dielectrically isolated from a gaseous dischargemedium between the conductors. The system utilizes a wave form generatorhaving at least one output transistor. Novel transformer-diode clampingmeans are provided to reverse bias the collector-base junction of theoutput transistor. The transformer-diode clamping means is responsive tothe removal of a turn-on signal and the saturation of the transistor toautomatically reverse bias the collector-base junction to provide asystem which produces a more effective wave form. The wave form in theembodiment shown is used as a sustaining voltage for cells in a gasdischarge display/- memory panel. This embodiment of the transformerdiode clamping means is particularly effective when connecting theoutput of the wave form generator to ground.

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m QLH CONTROL APPARATUS FOR SUPPLYING OPERATING POTENTIALS BACKGROUND OFTHE INVENTION In the Baker, et al. US. Pat. No. 3,499,167, issued Mar.3, 1970, there is disclosed a multiple discharge display and/or memorypanel which may be characterized as being of the pulsing discharge typehaving a gaseous medium, usually a mixture of two gases at a relativelyhigh gas pressure, in a thin gas chamber or space between opposeddielectric charge storage members which are backed by conductor arrays.The conductor arrays backing each dielectric member are transverselyoriented to define or locate a plurality of discrete discharge volumesor sites and constitute a discrete discharge unit. In some cases, thedischarge units may be additionally defined by physical structures suchas perforated glass plates and the like and in other cases capillarytubes and like structures may be used. In the above-identified patentapplication of Baker, et al., physical barriers and isolation membersfor discrete discharge sites have been eliminated. In such devices,charges (electrons and ions) produced upon ionization of the gas at aselected discharge site or conductor crosspoint, when proper operatingpotentials are applied to selected conductors thereof, are stored uponthe surfaces of the dielectric at the selected locations or sites andconstitute an electrical field opposing the electrical field whichcreated them. After a firing potential has been applied to initiate adischarge, the electrical field created by the charges stored upon thedielectric members aids in initiating subsequent momentary or pulsingdischarges on succeeding half-cycles of an applied sustaining potentialso that the applied sustaining potential, and hence the storage chargesindicate the previous discharge condition of a discharge unit or siteand can constitute an electrical memory.

In dynamic operation, in addition to the sustaining voltages, writingand erasing pulses may be superimposed on and algebraically added to thesustaining wave forms applied to selected transverse conductor pairs inthe conductor arrays to manipulate discharge conditions of dischargesites. Some of the preferred types of circuits for supplying thesustaining potentials, and for generating the manipulating pulses to beadded to the sustaining potentials, utilize output transistors which aredriven into deep saturation to abruptly switch the wave form from onepotential level to another. Difficulties have been encountered in thepast, in that when a transistor is turned on and driven into deepsaturation, it is difficult to bring the transistor out of saturationand turn it off quickly. This makes control of the shape of the trailingedge of the wave form difficult, may interfere with the addition ofmanipulating pulses, etc. and is undesirable.

Diode clamping circuits have been proposed and are useful in certainapplications for bringing the transistor out of saturation within thetime limits of those systems. However, as the switching speeds increaseand as the type of wave forms applied as sustaining potentials and asmanipulating pulses become more complex, the diode clamping circuit isnot suitable for all applications.

Accordingly, it is an object of this invention to provide animprovedsystem for supplyingoperating potentials to load devices,particularly wherein the load devices are of the gas dischargedisplay/memory type.

It is another object of this invention to provide im proved voltage waveform generating means which includes at least two sections, each of thesections having an output transistor to connect first and secondpotential levels to the load device. In a preferred embodiment an outputtransistor senses the removal of a turnon signal to the transistor andthe saturation of the transistor to automatically reverse bias acollector-base junction of the transistor enabling the transistor toturn off quickly.

It is a further object of this invention to provide improved controlapparatus for transistors which are operable to connect a load deviceinput to ground enabling a novel transformer-diode clamping circuit toautomatically bring the transistor out of saturation after flow ofdischarge currents from the load device and permit the transistor toturn off" more quickly.

SUMMARY OF THE INVENTION The invention is disclosed and described hereinin a system for supplying operating potentials to a gas dischargedisplay/memory device of the type disclosed and described in mycopending application filed concurrently with this application and alsoentitled Control Apparatus for Supplying Operating Potentials. A waveform generating means is shown which includes at least two sections, afirst of the sections being operative to connect a first potential levelto the output of the generator, while a second of the sections isoperative to connect a second potential level to the output, the outputbeing connected to conductors in the array of the gas discharge device,either directly or thru line to line isolation elements, such as diodes.

Each of the output sections preferably includes at least one outputtransistor means operating as a switching means between its respectivepotential level and the output of the wave form generating means. Eachof the transistors has a collector, base and emitter electrode and acollector-base junction.

Means are provided for selectively applying turn-on signals to the baseelectrodes of each of the output transistor means, the signals beingsufficient in magnitude to drive each of the output transistors intosaturation. Means may also be provided for selectively applying turn-offsignals to the output of one of the transistor means. Means responsiveto the turn-off signals for the one transistor means selectivelyestablishes current flow through the collector-base junction of thatoutput transistor to reverse bias the collector-base junction to bringthat transistor out of saturation and enable the output transistor toturn off quickly. This circuit is not shown in detail herein but isincluded herein by reference to my copending application notedhereinbefore.

Reverse bias establishing means are provided for both of the outputtransistors discussed herein, and each includes a transformer havingprimary and secondary windings, an isolating rectifier means, and meansfor connecting a reverse bias source to the primary winding of thetransformer. There are two embodiments of the reverse bias establishingmeans discussed herein, each useful in a particular application. Both ofthe reverse bias establishing means may be generically described ashaving at least one of the primary and secondary windings connected inacircuit across the collector-base junction of the output transistor withthe isolating rectifier means. The isolating rectifier means isconnected to prevent current flow from a collector electrode through oneor more windings of the transformer in response to potential differencesestablishing a forward bias across the collector-base junction.

The primary winding of the transformer of both of the reverse biasestablishing means may be generically described as being connected toreceive current from a reverse bias source which will induce a potentialon the secondary winding which will cause current flow through theisolating rectifier in a forward direction and through thecollector-base junction in a direction to reverse bias thecollector-base junction and discharge the minority carriers from thesaturated junction to enable the transistor to turn of quickly.

Specifically, the novel embodiment of the reverse bias establishingmeans described and disclosed herein has the primary winding connecteddirectly between one side of a reverse bias source through the isolatingrectifier to the collector electrode of the output transistor. Therectifier prevents current flow in the primary winding from thecollector electrode. The secondary winding is directly connected betweenthe base electrode and the other side of the reverse bias source so thatcurrent flow in the primary winding from the reverse bias source isautomatically enabled when the transistor becomes saturated and willinduce a voltage on the secondary winding which will reverse bias thecollector-base junction of the transistor.

There is also described means for selectively applying turn-on signalsto the base electrode of the output transistor of the preferredembodiment herein, which includes switching means responsive to turn-onsignal to connect a turn-on source to the output transistor. Theswitching means is interposed between a turn-on source and the baseelectrode of the output transistor. The bias source may be derived fromthe turn-on source, or vice versa, so that only a single such source ora single set of connections to such source is required.

' which:

FIG. 1 is a partially cut-away plan view of a gaseous dischargedisplay/memory panel as connected to a diagrammatically illustratedsource of operating potentials;

FIG. 2 is across-sectional view (enlarged, but not to proportional scalesince the thickness of the gas volume, dielectric members and conductorarrays have been enlarged for purposes of illustration) taken on lines 22 of FIG. 1;

FIG. 3 is a diagrammatic layout of a system for supplying sustainingvoltage for a gaseous discharge display/memory panel;

FIG. 4 is a graphical representation of cell sustaining voltage whichmay be supplied by the system of FIG. 3 and cell current flow inresponse to application of the sustaining voltage thereto and/or togaseous discharges;

FIG. 5 is a schematic diagram of a circuit embodying the teachings ofthis invention for supplying sustaining voltage to the row conductors ofthe panel; and

FIG. 6 is a graphical representation of the sustaining voltage suppliedby the apparatus of FIG. 5 in response to the graphically representedinput pulses from the row logic circuits.

FIG. 7 is a schematic diagram of the "PULL-UP CIR- CUIT of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention utilizes a pairof dielectric films 10 and 11 shown in FIG. 1 and 2 as separated by athin layer or volume of a gaseous discharge medium 12, the medium 12producing a copious supply of charges (ions and electrons) which arealternately collectable on the surfaces of the dielectric members atopposed or facing elemental or discrete areas X and Y defined by theconductor matrix on non-gas-contacting sides of the dielectric members,each dielectric member presenting large open surface areas and aplurality of pairs of elemental X and Y areas. While the electricallyoperative structural members such as the dielectric members 10 and 11and conductor matrixes I3 and 14 are all relatively thin (beingexaggerated in thickness in FIGS. 1 and 2) they are formed on andsupported by rigid nonconductive support members 16 and 17 respectively.

Typically, one or both of nonconductive support members 16 and 17 passlight produced by discharge in the elemental gas volumes. Usually, theyare transparent glass members and these members essentially define theoverall thickness and strength of the panel. For example, the thicknessof gas layer 12 as determined by spacer 15 is usually under 10 mils andtypically about 4 to 6 mils, dielectric layers 10 and 11 (over theconductors at the elemental or discrete X and Y areas) are usuallybetween 1 and 2 mils thick, and conductors 13 and 14 about 8,000angstroms thick. However, support members 16 and 17 are much thicker(particularly in large panels) so as to provide as much ruggedness asmay be desired to compensate for stresses in the panel. Support members16 and 17 also serve as heat sinks for heat generated by discharges andthus minimize the effect of temperature on operation of the device. Ifit is desired that only the memory function be utilized, then none ofthe members need be transparent to light.

Except for being nonconductive or good insulators the electricalproperties of support members 16 and 17 are not critical. The mainfunction of support members 16 and 17 is to provide mechanical supportand strength for the entire panel, particularly with respect to pressuredifferential acting on the panel and thermal shock. As noted earlier,they should have thermal expansion characteristics substantiallymatching the thermal expansion characteristics of dielectric layers 10and 11. Ordinary inch commercial grade soda lime plate glasses have beenused for this purpose. Other glasses such as low expansion glasses ortransparent devitrified glasses can be used provided they can withstandprocessing and have expansion characteristics substantially matchingexpansion characteristics of the dielectric coatings l0 and 11. Forgiven pressure differentials and thickness of plates, the stress anddeflection of plates may be determined by following standard Spacer 15may be made of the same glass material as dielectric films and 11 andmay be an integral rib formed on one of the dielectric members and fusedto the other members to form a bakeable hermetic seal enclosing andconfining the ionizable gas volume 12. However, a separate finalhermetic'seal may be effected by a high strength devitrified glasssealant S. Tubulation 18 is provided for exhausting the space betweendielectric members 10 and 11 and filling that space with the volume ofionizable gas. For large panels small bead-like solder glass spacerssuch as shown at 15B may be located between conductor intersections andfused to dielectric members 10 and 11 to aid in withstanding stress onthe panel and maintain uniformity of thickness of gas volume 12.

Conductor arrays 13 and 14 may be formed on support members 16 and 17 bya number of well-known processes, such as photoetching, vacuumdeposition, stencil screening, etc. In one embodiment, thecenterto-center spacing of conductors in the respective arrays is about17 mils. Transparent or semitransparent conductive material such as tinoxide, gold or aluminum can be used to form the conductor arrays andshould have a resistance less than about 1,000 ohms per linear inch ofconductor line, usually less than about 50 ohms per inch. Narrow opaqueelectrodes may alternately be used so that discharge light passes aroundthe edges of the electrodes to the viewer. It is important to select aconductor material that is not attacked during processing by thedielectric material.

It will be appreciated that conductor arrays 13 and 14 may be wires orfilaments of copper, gold, silver or aluminum or any other conductivemetal or material. For example l mil wire filaments are commerciallyavailable and may be used in the invention. However, formed in situconductor arrays are preferred since they may be more easily anduniformly placed on and adhered to the support plates 16 and 17.

Dielectric layer members 10 and 11 are formed of an inorganic materialand are preferably formed in situ as an adherent film or coating whichis not chemically or physically effected during bake-out of the panel.One such material is a solder glass such as Kimble SG-68 manufactured byand commercially available from the assignee of the present invention.

This glass has thermal expansion characteristics substantially matchingthe thermal expansion characteristics of certain soda-lime glasses, andcan be used as the dielectric layer when the support members 16 and 17are soda-lime glass plates. Dielectric layers 10 and 11 must be smoothand have'a dielectric strength of about 1,000 volts per mil and beelectrically homogeneous on a microscopic scale (e.g., no cracks,bubbles, crystals, dirt, surface films, etc.) In addition, the surfacesof dielectric layers 10 and 11 should be good photo-emitters ofelectrons in a baked-out condition. Alternatively, dielectric layers 10and 11 may be overcoated with materials designed to produce goodelectron emission, as in US. Pat. No. 3,634,719, issued to Roger E.Emsthausen. Of course, for an optical display at least one of dielectriclayers 10 and 11 should pass light generated on discharge and betransparent or translucent and, preferably, both layers are opticallytransparent.

The preferred spacing between surfaces of the dielectric films is about4 to 6 mils with conductor arrays 13 and 14 having center-to-centerspacing of about 17 mils.

The ends of conductors 14-1 14-4 and support member 17 extend beyond theenclosed gas volume 12 and are exposed for the purpose of makingelectrical connection to interface and addressing circuitry 19.Likewise, the ends of conductors 13-1 13-4 on support member 16 extendbeyond the enclosed gas volume 12 and are exposed for the purpose ofmaking electrical connection to interface and addressing circuitry 19.

As described in detail in the Baker, et al. US. Pat. No. 3,499,167, theentire gas volume can be initially conditioned for subsequent operationat substantially uniform firing potentials by the use of internal orexternal radiation to supply free electrons throughout the gas medium12.

Normal operation of a panel of the type described herein will bedescribed with reference to FIGS. 1, 2, 3, and 4, the interfacing andaddressing circuit indicated generally at 19 in FIG. 1 being'shown inmore detail in FIG. 3. Potentials having the wave forms 90 and 120 asshown in FIG. 3 are supplied from row and column sustainer circuitgenerators 80, 110 via row and column pulsing and addressing circuits100, 130 to conductor arrays 14, 13 in response to control pulses fromrow and column sections 72, 74, respectively of the logic controlcircuit 70. The resultant or composite potential wave form appearingacross each cell is indicated at 140 in FIG. 4 as a periodic wave formof an alternating character. The wave form 140 is derived for thepurpose of analysis of the operation of the panel by assuming that thewave forms 90 and 120 are spaced 180 apart or are oppositely phasedwithin the cycles of the periodic composite wave form 140, and that thewave form 120 is subtracted from the wave form )0.

1n the examples set forth in FIG. 3, the wave form 90 is a square wavewith a duration of less than one-half of the cycle defined by thecomposite wave form 140 and with a magnitude of +Vcc as will be shownhereinafter. Thus, more than 180 of the cycle of the composite wave form140 elapses between occurrences. The wave form 120 is also a square wavewith a duration of less than one-half of the cycle defined by thecomposite wave form 140, and with a magnitude of +Vcc, since thesustainer 110 may be identical to the sustainer 80.

The logic inputs to the sustainers 80 and 110 are phased 180 apart withrespect to the cycle of wave form 140. Therefore, the positive wave 120is produced when the positive wave is not being produced. When thepositive wave form is subtracted from the positive wave form 90, thewave form 120 appears to be negative in the composite wave form 140.

The voltage 90 from sustainer 80 constitutes approximately one-half ofthe sustaining voltage necessary to operate the panel, the remainingone-half which is necessary being supplied by voltage 120 phased 180 asnoted above with respect to the voltage 90. Thus, onehalf of thesustainer potential is applied to each of the row conductors 14 andone-half of the sustainer potential 140 is applied to each of the columnconductors 13. The sustainer circuits 80 and 110 advantageously have acommon ground so that the panel 10 floats with respect to ground.

Individual cells or discharge sites located by the crossing of selectedconductors or conductor arrays 14, 13 are manipulated by addingunidirectional voltage pulses at the proper time to each of thesustaining voltages on the selected conductors, which, when combined,are sufficient to exceed the firing potential for the selected cells andto initiate a sequence of discharges, one for each half-cycle of theapplied composite sustaining potential 140. By also properly timing suchunidirectional voltage pulses and applying them at a different portionin a cycle of the composite sustaining potential 140 to each of thesustaining voltages on the selected conductors, the sequence ofdischarges may be terminated. Thus, any individual discharge site may bemanipulated ON or OFF, by manipulation of the times of occurrences ofthe unidirectional voltage pulses.

The unidirectional voltage pulses are added to the sustainer voltages90, 120 on the selected conductors by the row and column pulsing andaddressing circuits 100, 130 in response to logic signals from the logiccontrol circuit 70 via leads 72-1 through 72-4 and 74-1 through 74-4,respectively, to select the conductor pairs for the individual cells.

Referring again to FIG. 4, it will be noted that between the positivehalf-cycles 90 and the negative halfcycles 120 of the composite waveform 140 there are provided plateaus 142, 144 at the apparent zerovoltage level indicating a brief time interval between the cessation ofthe generation of one-half cycle of the wave form 140 and the initiationof the other half-cycle of the wave form 140. These plateaus 142, 144may be provided to reduce interference between operation of variouscircuits for reasons that need not be detailed here.

However, the plateaus 142, 144 provide an opportunity to more clearlyshow what happens as the composite sustaining voltage 140 periodicallyalternates between the opposite polarities derived by subtracting thewave form 120 from the wave form 90. Referring to the graphicalrepresentation of cell current flow, shown in FIG. 4 in a timedrelationship with the composite wave form 140, it can be seen that asthe wave form goes from the negative level of the subtracted wave form120 to the zero level a cell displacement current flow occurs and isindicated by the positive current spikes 122. As the wave form 140 goesfrom the zero level to its positive level 90, a second cell displacementcurrent flow occurs and is indicated by the positive current spikes 92.

Similarly, as the wave form 140 goes from the positive level 90 to thezero level, a negative current spike 94 occurs. As the wave form 140goes from zero to the negative level of the subtracted wave form 120 anegative current spike 124 occurs.

Obviously, if separation plateaus 142 and 144 are not provided then thespikes 122, 92 and 94, 124 would occur at substantially the same timeand a single resultant larger current spike would occur when thecomposite wave form 140 reverses polarity.

If the cell in question has been manipulated to an ON condition ashereinbefore described then the cell will discharge when the differencebetween the wall voltage built up from a previous discharge and thesustainer potential exceeds the firing potential necessary to dischargethe cell. There then occurs a cell discharge current flow, indicated ascurrent spikes 146, 148 shown in dotted lines in FIG. 4.

It is desirable that the cell not see any appreciable voltage change inthe sustainer wave form during the wave form will continue to occur in amanner to maintain the cell ON in the condition required.

Row and column sustainer circuits 80, are advantageously constructedusing power transistors as output devices. It is desirable to be able toturn the power transistors ON and OFF as quickly as possible so that thetransition slope in the wave form controlled by the power transistors isas steep as possible. To turn a power transistor ON quickly it isnecessary to drive it with a comparatively large current pulse whichwill drive the transistor into deep saturation. The further thetransistor is driven into saturation the smaller the internal resistancewill be to the power output circuit it is controlling. If drivensufficiently far into saturation the displacement and discharge currentsof FIG. 4 may flow freely through the transistor and there will be verylittle voltage drop across the transistor during the time the cell isdischarging. Therefore, the voltage drop across the transistor will bevery small during the discharge cycle of the cell, will make very littlechange as a subtraction to the composite sustainer wave form, and willnot appreciably effect the transfer of wall charges during the dischargecycle of a cell.

Difficulties have been encountered, however, in that when the transistoris driven into deep saturation to reduce the wave form alteration to andbelow a desired level, it takes a longer time to turn the transistorOFF. This decreases the slope of the wave form being produced and maydelay or slow a voltage transition to a point which will interfere withthe proper panel operation. It also caused an excessive power loss,which can lead to component degradation due to unnecessary heating.

A diode clamping network has been used in the past to overcome theabove-discussed problem. In one embodiment a single diode is connectedto conduct in a forward direction from a clamping bias junction to thecollector electrode of a power transistor connected to a voltage beingcontrolled. Two diodes in series are connected to conduct in a forwarddirection from the clamping bias junction to the base electrode of thetransistor. The emitter electrode may be connected through a resistor tothe base electrode.

In operation, the just-discussed circuit receives a turn-on pulse havinga large magnitude to drive the transistor toward deep saturation,changing the configuration of the wave form being controlled andpermitting the free flow therethrough of the displacement current anddischarge current, if any, from the panel being controlled. Since thetransistor is going toward deep saturation the resistance offeredthereby to the discharge current results only in a voltage change in thecomposite sustaining wave form which is below a level which wouldsignificantly interfere with the transfer of the wall charges in anycells in the panel which are iON.9! I

If, in the embodiment of the diode clamping circuit being discussed, thecollector electrode is connected to an output voltage source beingcontrolled, when the flow of displacement and discharge current ceasesthere is no load on the transistor and if the transistor is still beingdriven hard, then deep saturation will occur because the collectorvoltage is lower than the base voltage.

To keep the transistor out of deep saturation the collector voltage iskept just above the base voltage by the diode clamping circuit. Thediode between the collec tor and the clamping bias junction is requiredto isolate the voltage wave form being controlled from the base of thetransistor. If the transistor requires a V voltage drop across thebase-emitter junction (and the resistor connecting the base and emitterelectrodes) to turn it on" then the isolating diode means is selected tohave a voltage drop in the forward direction in response to current flowthrough the clamping bias junction which is less than the voltage dropin the forward direction of the serially connected base diode means plusthe voltage drop across the base-emitter resistor in response to currentflow through the clamping bias junction.

Thus, if the isolating diode and any resistance associated therewith hasa voltage drop thereacross which is less than the clamping bias voltagenecessary at the clamping bias junction to keep the transistor on, thenthe collector voltage is equal to the clamping bias voltage minus theisolating diode voltage drop and is therefore larger than the basevoltage. The transistor is kept out of saturation and turns off when thedrive pulse is removed and stops conducting relatively quickly.

The clamping bias voltage is preferably applied to the clamping biasjunction at the same time that the drive pulse is removed from the baseof the transistor.

While the just-described diode clamping circuit has worked well in someapplications, it is desirable to be able to turn the power transistoroff even more quickly in certain applications. It is also desirable tobe able to use power transistors which have longer storage times (thelength of time a transistor stays in saturation without a drivingpotential applied) since the longer storage time transistors are lessexpensive. It is further desirable to be able to saturate the powertransistor as much as-possible, without interfering with the ability toturn the transistor off quickly, to reduce the internal resistance evenfurther than reduced with the diode clamping circuit, so that thevoltage drop across the transistor during flow of cell discharge currentis as low as possible.

Referring now to FIG. there is illustrated in detail a schematic diagramof a circuit which may be used as the sustainer wave form generator 80to produce the wave form 90 as shown in FIGS. 3 and 6. As notedhereinbefore, an identical circuit may be used to produce the wave form120.

The upper half of the circuit in FIG. 5 is illustrated in detail in FIG.7, which embodiment is also disclosed and discussed in the upper portionof FIG 5 of my copending US. Pat. application Ser. No. 313,480,simultaneously filed on Dec. 8, I972, with the instant application. Forthe purpose of avoiding obtaining a copy of the referenced applicationin order to understand the operation of this invention, there isincluded hegeinafter a description of the operation of an embodiment ofthe referenced application which is suitable for use here.

A bypass diode D4 is connected around the emittercollector electrodes ofthe output transistor of the wave form pull-up circuit section 81 topermit current flow to the panel when the column sustainer circuit 110is operative to provide the wave form 120 and for the flow of any of thedisplacement and any discharge currents that may be involved as theresult thereof. Similarly, a bypass diode D5 is connected around theemitter-collector electrodes of the power transistor Q8.

In operation of the circuit section 81, a short duration pull-up turn-onpulse 82 (see FIG. 6) is applied to terminal 82T on the base of a firstswitching transistor from the logic control via the lead 74UN (see FIG.3) to turn the first switching transistor on," thereby also turning asecond switching transistor on and permitting current flow from aturn-on source through the primary winding of an isolating transformer.A drive pulse is induced on the secondary winding of the isolatingtransformer causing current flow to turn an output power transistor ofcircuit section 81 on. The driving pulse induced in the secondary of theisolating transformer is of sufficient magnitude to drive the outputpower transistor very hard to bring the output terminal 92 to thevoltage level +Vcc as indicated in FIG. 6, and also leaves the outputpower transistor of circuit section 81 saturated.

Any time after the panel displacement and discharge current flow is, forthe most part, over a pull-up turn off pulse is applied to the baseelectrode of a third switching transistor via the lead 74UF from thelogic circuit 70. This pulse causes the third switching transistor toconduct, which, in turn, causes a fourth switching transistor to conductand provide a current flow in the primary winding of a transformer of atransformerdiode clamping circuit. Current flow is induced in thesecondary winding of the clamping circuit transformer causing apotential to be provided between the collector and the base of theoutput switching transistor which is higher at the collector than at thebase. The minority carriers of the saturated collector-base junction ofthe output power transistor of circuit section 81 are discharged througha diode connected in series with the secondary winding of the clampingtransformer. The transformer-diode circuit just described turns theoutput power transistor off very quickly allowing negative panel-addresspulses to also be applied quickly to the sustainer wave form 90, whichis a requirement in some addressing circuit schemes or techniques.

When the voltage is to be dropped at the output terminal 92 from thelevel of the potential +Vcc to ground or zero as illustrated in FIG. 6,a short duration pulldown turn-on pulse 86 is applied to the terminal86T connected to the base of the transistor Q6 via the lead 74DN fromthe logic circuit 70. This turns the transistor Q6 on allowingconduction through its emittercollector circuit thereby also turning thetransistor Q7 on." The bypass capacitor C1 enables bypassing of theemitter of the transistor Q7 and application of the driving pulse to thebase-emitter circuit of the power transistor Q8 turning it on veryquickly and deeply saturating the transistor. This reduces the voltageat the terminal 92 to ground level providing the zero output from thesustainer circuit as noted in FIG. 6.

The capacitor C1 is used in the pull-down driving circuit only, in thisinstance, because discharge current will immediately follow thepull-down transition of either the output transistor of the circuitsection 80 or transistor Q8, and the pull-down transistor Q8 has verylittle time to become saturated. So, the transistor Q8 requires a harderdrive than the pull-up output transistor of the circuit section 81 whichwill have the time provided by the plateau 142 to be driven deeply intosaturation before it will have to pass discharge current after it isturned on.

Alternatively, or in addition to the use of bypass capacitors, the valueof the resistance of the resistors R and/or R11 may be varied to varythe drive applied to transistors Q8.

When the transistor 08 is deeply saturated and the panel displacementand discharge current flow through the transistor O8 is over, for themost part, there will be very little voltage drop across thecollector-emitter circuit of the transistor Q8, both because theinternal resistance has been reduced by the hard driving pulse, andbecause there is little or no current flow through the internalresistance to cause a voltage drop. Therefore, when the voltage dropacross Q8 falls below the value of the reverse bias source +Vdc3, thediode D3 becomes forward biased and permits current flow through theprimary winding of the transformer T3 and the isolating diode D3 to thecollector of the power transistor Q8. This applies a potential to thecollector of the power transistor Q8 and current may flow from thecollector through the emitter and back to the other side of +Vdc3through a common ground connection. Current flow also occurs because ofthe voltage now induced on the secondary winding of the transformer T3which is connected to the base electrode of the power transistor 08. Thedeveloped potentials allows current to flow through the primary windingof the transformer T3, the isolating diode D3, the saturatedcollector-base junction of the power transistor Q8, and the secondarywinding of the transformer T3 to ground through a current limitingresistor R15 and then back to the other side of +Vdc3, discharging theminority carriers from the saturated collector-base junction, andturning off the power transistor Q8 very quickly.

As is evident by examining the drawings, only one source is now requiredsince the reverse bias source may be derived from the turn-on source, orvice versa. Therefore an extra source of supply and/or an extra set ofconnections to an additional source are not required.

The isolating rectifier D3 is preferably interposed between the primarywinding of T3 and the collector electrode of Q8, rather than between theprimary winding and the reverse bias source +Vdc3 so that anypossibility of current flow from the primary winding as a result ofcurrent flow in charging the primary to secondary capacitance does notflow to the secondary as it would if the primary swung with the output.

It should be noted that there will then be no significant current flowthrough the secondary winding of the transformer T3 from the drivingpulses for the transistor Q8, since there is no current flow through theprimary winding of transformer T3 until the reverse bias on the diode D3is removed. Therefore, a high impedance will be reflected to thesecondary winding and the driving current will flow through the base ofthe transistor Q8 and the resistor R11, respectively.

It should be noted that logic leads 72DF and 74DF from the logic circuit70 to the sustainer circuits 80, 110 are not needed for the embodimentillustrated in FIG. 5. There is no need for a pull-down turn-off logicpulse when using the present invention, because of the automatic sensingand acting capabilities of the novel circuit of this invention. Thiscircuit thus saves components and timing logic.

It should also be noted that a mirror image type modification of thecircuit illustrated in FIG. 5 may be constructed to produce negativepulse outputs 90 and 120 rather than the positive pulses as shown. Thatis, the signal, bias, and supply voltages would have oppositepolarities, while P-N-P type transistors would be substituted for N-P-Ntype transistors (and vice versa), and the connections of the diodes andthe transformers of the clamping circuits would be reversed wherenecessary to enable the reverse biasing of saturated collector-basejunctions to bring the clamped transistors out of saturation at adesired time.

Phasing of the negative logic signals from section 74 of units on leads74UN, 74UF, and 74DN, with spacings in a composite wave form cycle withrespect to the negative logic signals 72UF, 72UN, and 72DN, would alsobe obvious to obtain the resultant or composite cell sustainer voltagewave form illustrated in FIG. 4.

It should also be noted that combinations of positive and negativesustainer wave form generator circuits may be used in certainapplications.

There have thus been described and disclosed a transformer-diodeclamping circuit which may be used to turn output power transistors ofafter a very heavy turn-on drive pulse, enabling the power transistor tobe turned off in a fraction of the normal storage time for such devices.This enables a sustainer performance to meet and match the very fastswitching speed and high current requirements of newly developeddisplay/memory panels, as well as prior art panels. The very fast, highvoltage, high current switching of the apparatus disclosed herein faroutperforms the present prior art devices. The use of thetransformerdiode clamp described herein also permits greater flexibilityin unique logic address requirements. The present invention may also beused to take advantage of gaseous mediums which are presently beingtested and which exhibit much faster discharge times than past mediums.

What is claimed is: v

1. In a system for supplying operating potential to a load devicewherein at least two transversely oriented conductors are dielectricallyisolated from a gas discharge medium between said conductors, comprisinga. voltage wave form generator means having an output means adapted tobe connected to a transverse conductor;

b. said wave form generating means including at least two sections, afirst of said sections being operative to connect a first point at afirst potential level to said output means while a second of saidsections is operative to connect a second point at second potentiallevel different from said first potential level to said output means;

c. one of said output sections including an output transistor connectedas a switching means, said transistor having collector, base, andemitter electrodes and a collector-base junction, the emitter electrodeto collector electrode current path through said transistor beingconnected in series between said output means and the point at apotential level associated with said one of said output sections;

d. means for selectively applying turn-on signals to the base electrodeof said output transistor means, said signals being sufficient inmagnitude to drive said transistor means into saturation; and

e. means responsive to saturation of said transistor and the removal ofa turn-on signal from the base electrode for establishing current flowthroughsaid collector-base junction of said transistor means to reversebias said collector-base junction to enable said transistor to turn offquickly; I

1'. said reverse bias establishing means including a transformer havingprimary and secondary windings, an isolating rectifier means, and meansfor connecting one side of a reverse bias source to said primary windingof said transformer;

g. said primary winding being connected in series with said isolatingrectifier means between said bias source connecting means and saidcollector electrode of said transistor means, said isolating rectifierbeing connected in said series circuit to be reverse biased by potentiallevels on said collector electrode which are greater in magnitude thanthat of the reverse bias source thereby preventing current flow fromsaid collector electrode through said primary winding;

h. said secondary winding being connected between said base electrode ofsaid transistor and the other side of the reverse bias source, theemitter electrode of said transistor having a circuit connection to saidother side of said reverse bias source;

. the attainment of an on condition of said transistor means wherein theinternal resistance of the collector-emitter circuit drops below apredetermined value which, in combination with current flow therethroughfrom the output potential level being controlled, provides a voltagedrop across said emitter-collector circuit which is less than thepotential of the reverse bias source enabling current flow from saidreverse bias source through said primary winding and said isolatingrectifier means in the forward direction to said collector electrode;

means of said wave form generator means to a ground level potential toenable rapid discharge of any potentials derived from the load device toground, thereby j. current flow in said primary winding from saidreverse bias source inducing a voltage on said secondary winding whichcauses current flow through said collector-base junction in a directionto reverse bias said collector-base junction and discharge excessminority carriers from the saturated junction to enable said transistorto turn off quickly when a turn-on signal is removed from the baseelectrode.

2. A system as defined in claim 1 wherein said isolating rectifier meansis interposed between said primary winding and said collector electrode,thus preventing current flow from said primary winding to said collectorelectrode when the potential on said collector electrode is higher thanthat of the reverse bias source thereby reflecting a high impedance tosaid secondary winding and preventing current flow therethrough inresponse to the application of a turn-on signal to said base electrode.

3. A system as defined in claim 1, in which a. said means forselectively applying turn-0n signals includes a turn-on source andswitching means responsive to a turn-on signal for connecting saidturn-on source to said base electrode of said transistor means, andwhich further includes b. means for deriving one of said turn-on andreverse bias sources from the other, thereby requiring the provision ofonly one such source for the control of said transistor.

4. A system as defined in claim 1 in which said one of the outputsections is operable to connect the output enabling said primarywinding-isolating rectifier combination to rapidly sense the requiredlow voltage drop across the emitter-collector circuit of said transistorand initiate the establishment of reverse bias across saidcollector-base junction and enable said transistor to turn off quicklywhen a turn-on signal is removed from the base electrode.

5. In a system for supplying operating potential to a load devicewherein at least two transversely oriented conductors are dielectricallyisolated from a gas discharge medium between said two conductors,comprising a. voltage wave form generating means adapted to be connectedto a transverse conductor;

b. said wave form generating means including at least one transistormeans operating as a switching means between a point at an operatingpotential and a transverse conductor, said transistor means havingcollector, base, and emitter electrodes with collector-base andbase-emitter junctions;

c. means for applying a turn-on signal to said base electrode having amagnitude sufficient to turn said transistor on and drive saidtransistor into a saturated condition; and

d. means for selectively establishing current flow through saidcollector-base junction to reverse bias said junction;

e. said reverse bias establishing means including a transformer havingprimary and secondary windings, an isolating rectifier means, and meansfor connecting a reverse bias source to said primary winding of saidtransformer;

f. said primary winding being connected in a series circuit with saidisolating rectifier means between said bias source connecting means andsaid collector electrode of said transistor means, said isolatingrectifier means being connected in said series circuit to preventcurrent flow in said primary winding from said collector electrode;

g. said secondary winding being connected between said base electrode ofsaid transistor and the other side of the reverse bias source, theemitter electrode of said transistor having a circuit connection to saidother side of said reverse bias source;

h. the attainment of an on condition of said transistor means whereinthe internal resistance of the collector-emitter circuit drops below apredetermined value which, in combination with current flow therethorughfrom the output being controlled, provides a voltage drop across saidemittercollector circuit which is less than the potential of the reversebias source enabling current flow from said reverse bias source throughsaid primary winding and said isolating rectifier means in the forwarddirection to said collector electrode;

. current flow in said primary winding from said reverse bias sourceinducing a voltage on said secondary winding which causes current flowthrough said collector-base junction in a direction to reverse bias saidcollector-base junction and discharge excess minority carriers from thesaturated junction to enable said transistor to turn off quickly when atun-on signal is removed from the base electrode.

6. A system as defined in claim 5 in which a. said means for applying aturn-on signal includes a turn-on source and switching means responsiveto a turn-on signal for connecting said turn-on source to said baseelectrode of said transistor means, and which further includes b. meansfor deriving one of said turn-on and reverse bias sources from theother, thereby requiring the provision of only one such source for thecontrol of said transistor.

7. A system as defined in claim 5 in which said output transistor meansis operable to connect the output means of said wave form generatormeans to a ground level potential to enable rapid discharge of anypotentials derived from the load device to ground, thereby enabling saidprimary winding-isolating rectifier combination to rapdily sense therequired low voltage drop across the emitter-collector circuit of saidtransistor and initiate the establishment of reverse bias across saidcollector-base junction and enable said transistor to turn off quicklywhen a turn-on signal is removed from the base electrode.

8. Control apparatus, comprising a. transistor means having collector,base, and emitter electrodes with collector-base and base-emitterjunctions between said electrodes;

b. means for connecting a turn-on source to provide a driving signal tosaid base electrode having a magnitude sufficient to turn saidtransistor on and drive said transistor into a saturated condition; and

0. means responsive to saturation of said transistor and the removal ofa turn-on signal from the base electrode for establishing current flowthrough said collector-base junction of said transistor means to reversebias said collector-base junction to enable said transistor to turn offquickly;

d. said reverse bias establishing means including a transformer havingprimary and secondary windings, an isolating rectifier means, and meansfor connecting one side of a reverse bias source to said primary windingof said transformer;

e. said primary winding being connected in series trode of saidtransistor having a circuit connection to said other side of saidreverse bias source;

g. the attainment of an on" condition of said transistor means whereinthe internal resistance of the collector-emitter circuit drops below apredetermined value which, in combination with current flow therethroughfrom the output being controlled, provides a voltage drop across saidemittercollector circuit which is less than the potential of the reversebias source enabling current flow from said reverse bias source throughsaid primary winding and said isolating rectifier means in the forwarddirection to said collector electrode;

h. current fiow in said primary winding from said reverse bias sourceinducing a voltage on said secondary winding whcih causes current flowthrough said collector-base junction in a direction to reverse bias saidcollector-base junction and dis charge excess minority carriers from thesaturated junction to enable said transistor to turn off quickly when aturn-on signal is removed from the base electrode.

9. A system as defined in claim 8 wherein said isolating rectifier meansis interposed between said primary winding and said collector electrode,thus preventing current flow from said primary winding to said collectorelectrode when the potential on said collector electrode is higher thanthat of the reverse bias source thereby reflecting a high impedance tosaid secondary winding and preventing current flow therethorugh inresponse to the application of a turn-on signal to said base electrode.

10. A system as defined in claim 8 in which a. said means forselectively applying turn-on signals includes a turn-on source andswitching means responsive to a turn-on signal for connecting saidturn-on source to said base electrode of said transistor means, andwhich further includes b. means for deriving one of said turn-on andreverse bias sources from the other, thereby requiring the provision ofonly one such source for the control of said transistor.

11. A system as defined in claim 8 in which said output transistor isoperable to connect a potential level input to a load device to a groundlevel potential to enable rapid discharge of any potentials derived fromthe load device to ground, thereby enabling said primarywinding-isolating rectifier combination to rapidly sense the requiredlow voltage drop across the emittercollector circuit of said transistorand initiate the establishment of reverse bias across saidcollector-base junction and enable said transistor to turn off quicklywhen a turn-on signal is removed from the base electrode.

1. In a system for supplying operating potential to a load devicewherein at least two transversely oriented conductors are dielectricallyisolated from a gas discharge medium between said conductors, comprisinga. voltage wave form generator means having an output means adapted tobe connected to a transverse conductor; b. said wave form generatingmeans including at least two sections, a first of said sections beingoperative to connect a first point at a first potential level to saidoutput means while a second of said sections is operative to connect asecond point at second potential level different from said firstpotential level to said output means; c. one of said output sectionsincluding an output transistor connected as a switching means, saidtransistor having collector, base, and emitter electrodes and acollector-base junction, the emitter electrode to collector electrodecurrent path through said transistor being connected in series betweensaid output means and the point at a potential level associated withsaid one of said output sections; d. means for selectively applyingturn-on signals to the base electrode of said output transistor means,said signals being sufficient in magnitude to drive said transistormeans into saturation; and e. means responsive to saturation of saidtransistor and the removal of a turn-on signal from the base electrodefor establishing current flow through said collector-base junction ofsaid transistor means to reverse bias said collector-base junction toenable said transistor to turn off quickly; f. said reverse biasestablishing means including a transformer having primary and secondarywindings, an isolating rectifier means, and means for connecting oneside of a reverse bias source to said primary winding of saidtransformer; g. said primary winding being connected in series with saidisolating rectifier means between said bias source connecting means andsaid collector electrode of said transistor means, said isolatingrectifier being connected in said series circuit to be reverse biased bypotential levels on said collector electrode which are greater inmagnitude than that of the reverse bias source thereby preventingcurrent flow from said collector electrode through said primary winding;h. said secondary winding being connected between said base electrode ofsaid transistor and the other side of the reverse bias source, theemitter electrode of said transistor having a circuit connection to saidother side of said reverse bias source; i. the attainment of an''''on'''' condition of said transistor means wherein the internalresistance of the collector-emitter circuit drops below a predeterminedvalue which, in combination with current flow therethrough from theoutput potential level being controlled, provides a voltage drop acrosssaid emittercollector circuit which is less than the potential of thereverse bias source enabling current flow from said reverse bias sourcethrough said primary winding and said isolating rectifier means in theforward direction to said collector electrode; j. current flow in saidprimary winding from said reverse bias source inducing a voltage on saidsecondary winding which causes current flow through said collector-basejunction in a direction to reverse bias said collector-base junction anddischarge excess minority carriers from the saturated junction to enablesaid transistor to turn off quickly when a turn-on signal is removedfrom the base electrode.
 2. A system as defined in claim 1 wherein saidisolating rectifier means is interposed between said primary winding andsaid collector electrode, thus preventing current flow from said primarywinding to said collector electrode when the potential on said collectorelectrode is higher than that of the reverse bias source therebyreflecting a high impedance to said secondary winding and preventingcurrent flow therethrough in response to the application of a turn-onsignal to said base electrode.
 3. A system as defined in claim 1, inwhich a. said means for selectively applying turn-on signals includes aturn-on source and switching means responsive to a turn-on signal forconnecting said turn-on source to said base electrode of said transistormeans, and which further includes b. means for deriving one of saidturn-on and reverse bias sources from the other, thereby requiring theprovision of only one such source for the control of said transistor. 4.A system as defined in claim 1 in which said one of the output sectionsis operable to connect the output means of said wave form generatormeans to a ground level potential to enable rapid discharge of anypotentials derived from the load device to ground, thereby enabling saidprimary winding-isolating rectifier combination to rapidly sense therequired low voltage drop across the emitter-collector circuit of saidtransistor and initiate the establishment of reverse bias across saidcollector-base junction and enable said transistor to turn off quicklywhen a turn-on signal is removed from the base electrode.
 5. In a systemfor supplying operating potential to a load device wherein at least twotransversely oriented conductors are dielectrically isolated from a gasdischarge medium between said two conductors, comprising a. voltage waveform generating means adapted to be connected to a transverse conductor;b. said wave form generating means including at least one transistormeans operating as a switching means between a point at an operatingpotential and a transverse conductor, said transistor means havingcollector, base, and emitter electrodes with collector-base andbase-emitter junctions; c. means for applying a turn-on signal to saidbase electrode having a magnitude sufficient to turn said transistor onand drive said transistor into a saturated condition; and d. means forselectively establishing current flow through said collector-basejunction to reverse bias said junction; e. said reverse biasestablishing means including a transformer having primary and secondarywindings, an isolating rectifier means, and means for connecting areverse bias source to said primary winding of said transformer; f. saidprimary winding being connected in a series circuit with said isolatingrectifier means between said bias source connecting means and saidcollector electrode of said transistor means, said isolating rectifiermeans being connected in said series circuit to prevent current flow insaid primary winding from said collector electrode; g. said secondarywinding being connected between said base electrode of said transistorand the other side of the reverse bias source, the emitter electrode ofsaid transistor having a circuit connection to said other side of saidreverse bias source; h. the attainment of an ''''on'''' condition ofsaid transistor means wherein the internal resistance of thecollector-emitter circuit drops below a predetermined value which, incombination with current flow therethorugh from the output beingcontrolled, provides a voltage drop across said emitter-collectorcircuit which is less than the potential of the reverse bias sourceenabling current flow from said reverse bias source through said primarywinding and said isolating rectifier means in the forward direction tosaid collector electrode; i. current flow in said primary winding fromsaid reverse bias source inducing a voltage on said secondary windingwhich causes current flow through said collector-base junction in adirection to reverse bias said collector-base junction and dischargeexcess minority carriers from the saturated junction to enable saidtransistor to turn off quickly when a tun-on signal is removed from thebase electrode.
 6. A system as defined in claim 5 in which a. said meansfor applying a turn-on signal includes a turn-on source and switchingmeans responsive to a turn-on signal for connecting said turn-on sourceto said base electrode of said transistor means, and which furtherincludes b. means for deriving one of said turn-on and reverse biassources from the other, thereby requiring the provision of only one suchsource for the control of said transistor.
 7. A system as defined inclaim 5 in which said output transistor means is operable to connect theoutput means of said wave form generator means to a ground levelpotential to enable rapid discharge of any potentials derived from theload device to ground, thereby enabling said primary winding-isolatingrectifier combination to rapdily sense the required low voltage dropacross the emitter-collector circuit of said transistor and initiate theestablishment of reverse bias across said collector-base junction andenable said transistor to turn off quickly when a turn-on signal isremoved from the base electrode.
 8. Control apparatus, comprising a.transistor means having collector, base, and emitter electrodes withcollector-base and base-emitter junctions between said electrodes; b.means for connecting a turn-on source to provide a driving signal tosaid base electrode having a magnitude sufficient to turn saidtransistor on and drive said transistor into a saturated condition; andc. means responsive to saturation of said transistor and the removal ofa turn-on signal from the base electrode for establishing current flowthrough said collector-base junction of said transistor means to reversebias said collector-base junction to enable said transistor to turn offquickly; d. said reverse bias establishing means including a transformerhaving primary and secondary windings, an isolating rectifier means, andmeans for connecting one side of a reverse bias source to said primarywinding of said transformer; e. said primary winding being connected inseries with said isolating rectifier means between said bias sourceconnectng means and said collector electrode of said transistor means,said isolating rectifier being connected in said series circuit to bereverse biased by potential levels on said collector electrode which aregreater in magnitude than that of the reverse bias source therebypreventing current flow from said collector electrode through saidprimary winding; f. said secondary winding being connected between saidbase electrode of said transistor and the other side of the reverse biassource, the emitter electrode of said transistor having a circuitconnection to said other side of said reverse bias source; g. theattainment of an ''''on'''' condition of said transistor means whereinthe internal resistance of the collector-emitter circuit drops below apredetermined value which, in combination with current flow therethroughfrom the output being controlled, provides a voltage drop across saidemitter-collector circuit which is less than the potential of thereverse bias source enabling current flow from said reverse bias sourcethrough said primary winding and said isolating rectifier means in theforward direction to said collector electrode; h. current flow in saidprimary winding from said reverse bias source inducing a voltage on saidsecondary winding whcih causes current flow through said collector-basejunction in a direction to reverse bias said collector-base junction anddischarge excess minority carriers from the saturated junction to enablesaid transistor to turn off quickly when a turn-on signal is removedfrom the base electrode.
 9. A system as defined in claim 8 wherein saidisolating rectifier means is interposed between said primary winding andsaid collector electrode, thus preventing current flow from said primarywinding to said collector electrode when the potential on said collectorelectrode is higher than that of the reverse bias source therebyreflecting a high impedance to said secondary winding and preventingcurrent flow therethorugh in response to the application of a turn-onsignal to said base electrode.
 10. A system as defined in claim 8 inwhich a. said means for selectively applying turn-on signals includes aturn-on source and switching means responsive to a turn-on signal forconnecting said turn-on source to said base electrode of said transistormeans, and which further includes b. means for deriving one of saidturn-on and reverse bias sources from the other, thereby requiring theprovision of only one such source for the control of said transistor.11. A system as defined in claim 8 in which said output transistor isoperable to connect a potential level input to a load device to a groundlevel potential to enable rapid discharge of any potentials derived fromthe load device to ground, thereby enabling said primarywinding-isolating rectifier combination to rapidly sense the requiredlow voltage drop across the emitter-collector circuit of said transistorand initiate the establishment of reverse bias across saidcollector-base junction and enable said transistor to turn off quicklywhen a turn-on signal is removed from the base electrode.